DESCRIPTION (Applicant's Abstract): Impressed by the results of a particularly successful and oversubscribed international meeting on Molecular Clocks held at the Juan March Foundation in May of 1998, a Keystone meeting on the subject is proposed for 2001. The sub-areas to be represented include (1) Molecular and genetics studies of circadian behavioral rhythms in animal systems, with emphasis on newly identified genes, the strong homologies among clock genes in the animal kingdom, and their mechanisms of action. (2) The molecular pathways that afford resetting of clocks and the sleep/wake cycle in response to light. Our understanding of the molecular mechanisms associated with phototransduction and clock gene responses has grown significantly in just the past year. The role of cryptochromes, which act as circadian photoreceptors in some systems, is now widely studied. (3) Regulation of wake/sleep behavior. Biochemical strategies for conveying signals from molecular clocks to timed behavior have been clarified in the past year. (4) Genetic control of human wake/sleep cycles. The first hereditary variations in human circadian rhythms were reported last year as well as a partial molecular description of narcolepsy in mammalian models. (5) Plant, fungal, and bacterial clocks, and modeling molecular oscillators. Non-animal model systems continue to provide some of our greatest insights into biochemical mechanisms underlying circadian [clocks].